Ekaterina A. Vyacheslavova

In this work, the physical origin of the persistent photoconductivity (PPC) effect in InP films synthesized by plasma-enhanced atomic layer deposition (PE-ALD) at 380 °C was investigated. Cross-sectional TEM confirmed the formation of a nanocrystalline cubic InP layer on Si, while Raman spectroscopy revealed comparable crystalline characteristics for films grown on Si and fused silica substrates. The photocurrent relaxation kinetics was well described by a stretched-exponential function, indicating a broad distribution of characteristic relaxation times associated with heterogeneous trapping and recombination processes. A significant difference was revealed between the activation energy of equilibrium electron transport (0.114 ± 0.003 eV) and the macroscopic recombination barrier for nonequilibrium carriers (0.270 ± 0.058 eV). Hall-effect measurements showed that the PPC is predominantly associated with an increase in electron concentration, rather than changes in carrier mobility. The long lifetime of the photoexcited state is consistent with a barrier-mediated mechanism of spatial separation of electron hole pairs associated with grain boundaries.

The fabrication of periodical GaN/InP structures on Si with a wide layer thickness variation (from submonolayer digital alloys to multilayer stacks) using low-temperature plasma technology is explored in the paper. The proposed technology, which combines the approaches of plasma-enhanced chemical vapor deposition (PECVD) and atomic-layer deposition, was realized at 380 °C using a standard capacitively coupled plasma PECVD reactor. Trimethylindium, trimethylgallium, phosphine, and nitrogen (N2) were used as sources of In, Ga, P, and N, respectively. A series of GaN/InP periodical structures were grown on an Si (001) substrate with a previously deposited thin (7 nm) GaP buffer layer. A structure grown as submonolayer digital alloys (a short-period superlattice with GaN and InP thicknesses of 0.3 and 0.6 nm) exhibits a crystal structure consisting of both microcrystalline and epitaxially oriented grains that follow the orientation of the Si substrate. The vertical size of the grains corresponds to the total GaN/InP periodical structure’s thickness. However, with an increase in the GaN barrier layer thickness to 1.5–3 nm, the GaN undergoes amorphization. This leads to the formation of a layered structure containing misoriented nanocrystalline InP layers embedded between amorphous GaN layers. This effect is associated with significant incorporation of phosphorus into GaN layers, which are formed using a N2 + H2 gas mixture plasma. Indeed, the H2 plasma used for GaN deposition interacts with the phosphorus deposited on the chamber wall during the previous InP step. The discovered issue should be taken into account for plasma technology development of multilayer structures, which included a combination of III-nitride/III-phosphide.

Boron phosphide (BP) thin films are potential selective contact layers for photovoltaic (PV) devices. However, lower deposition temperatures are preferred in the fabrication of many PV devices, such as solar cells, to reduce their cost. Here, boron phosphide layers were grown on silicon (100) substrates using the standard plasma-enhanced chemical vapor deposition (PECVD) and time-modulated PECVD methods with trimethylboron [B(CH3)3, TMB] and phosphine precursors. The effect of plasma power and Ar addition on structural properties and chemical composition is investigated, while material properties are analyzed by transmission electron microscopy. Chemical characterization by the electron diffraction x-ray spectroscopy method showed high carbon content in the BP layer. Electron energy loss spectroscopy demonstrated almost stoichiometric B and P (1:1) content. Raman spectroscopy of annealed samples showed an increase in carbon-related peaks, therefore indicating that annealing does not lead to the crystallization of boron phosphide. Thus, using TMB as a precursor of boron leads to carbon contamination in both standard and time-modulated modes. Optical emission spectroscopy showed that the low-temperature growth of BP without plasma (Ar or phosphine) assistance using TMB is impossible. We conclude that there is a need to investigate other boron precursors for boron phosphide low-temperature growth to avoid carbon contamination in BP films.

In this paper, we propose a method for the formation of efficient photoconverters which optical band gap decreases due to the introduction of impurities (gold nanoparticles) into the oxide. Gold nanoparticles can act both as noticeable levels in the band gap and as plasmonic particles. The use of 2D geometry in this case allows you to significantly increase the effective transformation surface. Photo-induced current transfer through nanocomposite structures consisting SiO 2 layers activated with gold nanoparticles (AuNP) are under investigation. AuNPs are situated on top of SiO 2 nano-pillars. Nano-pillar array with AuNPs is prepared by previously described two-step technique using plasma etching. Optical and electric characteristics of these structure are investigated.

The aim of this work is a silicon nanowire-based selective vapor sensing of ammonia (NH 3 ) and hydrochloric acid (HCl) via electrical impedance spectroscopy (EIS). Developed highly sensitive silicon sensors could be used for indirect selective analysis of liquid solution composition containing NH 3 and HCl. We use Si nanowires (Si NWs) obtained with cryogenic plasma etching with high aspect ratio providing large adsorption surface area to provide enhanced sensitivity. The NWs are placed on a contact platform and EIS is used to detect the analytes. The development of three different types of sensors based on Si NWs, Si NWs treated with hydrofluoric acid (HF), and Si NWs decorated with silver nanoparticles (Ag NPs) showcases an optimization effort to enhance the sensor's performance. Furthermore, this work proposes a novel approach for interpreting the electrical impedance spectroscopy (EIS) spectra. Instead of analyzing the response solely in terms of impedance or frequency, the proposed approach suggests considering the response in a frequency-resistance F(R) space. This innovative analysis method offers a new perspective for understanding and interpreting the sensor's behavior and response characteristics. By visualizing the response in the F(R) space, it becomes possible to uncover patterns and correlations that might be overlooked by traditional analysis methods.

The influence of Ar gas additives on ≪black silicon≫ formation is shown in this work. The way to achieve the conical shape of Si texture using low Ar dilution is demonstrated. Also, a possibility of silicon nanowire width reduction keeping a high density of array is shown. No damage to the Si structure caused by Ar plasma was detected. The introduction of Ar into the plasma also does not affect electrical properties. The lifetime value after cryogenic etching with 5 sccm Ar flow remains at the same level of 0.7 ms. The resulting black silicon has a low total reflectance of 1 ± 0.5% in the range of 450–1000 nm in the overall 100 mm Si wafer surface.